This application is based on Patent Application No. 2000-177506 filed Jun. 13, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a method of writing a data write/read head positioning servo signal written to the magnetic recording disk by the magnetic transfer technology in the hard disk drive (HDD) using as a recording material a magnetic film which is normally used as a mainstream of an external storage device of a computer, and more specifically to a method of recognizing a master disk positioning mark.
2. Description of the Prior Art
It is well known that a hard disk drive device records and reads data while a magnetic head is floating while keeping interval of several tens nano-meter on the revolving magnetic recording disk using a floating mechanism referred to as a slider. The bit information on the magnetic disk is stored on the data track concentrically provided on the disk, and the data record/read head records and reproduces data on the target data track on the disk surface by quickly moving and positioning the head.
On the magnetic recording disk surface, a positioning signal (servo signal) for detection of the relative position between the head and the data track is concentrically written, and the head for recording and reproducing data detects the position of itself at predetermined time intervals. After incorporating the recording disk into the HDD device, the servo signal is written using a dedicated device referred to as a servo track writer so that the center of the servo write signal cannot be deviated from the center of the disk (or the center of the orbit of the head).
Currently, the recording disk has the recording density of about 20 Gbits/in2 at the development stage, and the recording capacity increases at the rate of 60% annually. With the above mentioned progress, the density of a servo signal for detection of the position of the head itself also increases, and the writing time of a servo signal has been increased year by year. An increasing writing time of the servo signal is a main factor of reducing the productivity of the HDD, thereby increasing the entire cost.
Recently, to replace the system of writing the servo signal using the signal write head of the above mentioned servo track writer, the technology has been developed to collectively write servo signals by a magnetic transfer, and thereby remarkably shorten the servo information writing time. FIGS. 7A, 7B, 7C, 8A and 8B illustrate the magnetic transfer technology.
FIG. 7A shows the process of moving a permanent magnet on the surface of a magnetic recording disk 3 while keeping a predetermined interval (1 mm or shorter). The arrow recorded on the magnetic layer shown in FIG. 7A shows a moving path of the permanent magnet, and the magnetic layer is evenly magnetized radiantly. This process is referred to as an initial demagnetizing process.
FIG. 7B shows the process of aligning a magnetic transfer master disk 7 (hereinafter referred to as a master disk) by setting it on the magnetic recording disk 3.
FIG. 7C shows the magnetic transfer process performed by setting the master disk 7 as choereing the surface of the magnetic recording disk 3 and moving the magnetic transfer permanent magnet along the moving path (indicated by the arrow shown in FIG. 7C).
FIG. 8A shows the initial demagnetizing process. The process of a permanent magnet 42 of a head 41 moving on the surface of a magnetic recording disk 3 while keeping a predetermined interval (1 mm or shorter) is shown from the sectional portion of a substrate 31. A magnetic layer 32 filmed on the substrate 31 is not initially magnetized in a predetermined direction, but can be magnetized in a predetermined direction by a magnetic field leaking from the gap of the permanent magnet 42.
FIG. 8B shows a transfer pattern writing process for performing a magnetic transfer. As shown in FIG. 8B, the master disk 7 has the structure of a soft magnetic film 8 (Co type soft magnetic film in FIG. 8B) embedded into the surface of a silicon substrate 71 touching the surface of a medium. As shown in FIG. 8B, if there is the substrate 71 embedded a pattern of the soft magnetic film 8 between the permanent magnet 42 of the head 41 and the magnetic recording disk 3, the magnetic field (the direction of the transfer signal write magnetic field is opposite the direction of the demagnetized field) leaking from the permanent magnet 42 and passing through the silicon substrate 71 can pass through the silicon substrate 71 again and magnetize the magnetic layer 32 of the magnetic recording disk 3 at the point where there is no soft magnetic film 8, but it passes through the soft magnetic film 8 at the point where there is a soft magnetic pattern 8 such that a magnetic path can be formed with smaller magnetic resistance. Therefore, at the point where there is the soft magnetic film 8, the magnetic field leaking from the silicon substrate 71 is small, and no magnetic write is newly made. With the above mentioned mechanism, a magnetic transfer of a servo signal is performed.
To perform such above mentioned magnetic transfer, it is necessary for the center of the servo pattern (soft magnetic pattern embedded into the surface of the master disk) embedded into the master disk 7 to match the center of the magnetic medium 3 (magnetic recording disk). To make these centers match each other, it is necessary to determine the positions of the center of the magnetic medium 3 and the center of the servo pattern on the master disk 7 respectively. The method of confirming the central position of the magnetic medium 3 can be realized by revolving the medium held by a chuck with a laser light illuminated on the outer edge of the medium, and determining the amount of deviation of the center of the chuck from the center of the medium based on the variation of the reflected light from the outer edge.
FIG. 9 illustrates the method of recognizing the position of the center of the soft magnetic pattern 8 on the master disk 7 by the conventional technology. The master disk 7 is moved closer to the magnetic recording disk 3 held by a chuck 4, the position of the master disk 7 is recognized using a positioning mark 9 (a circular pattern (200-300 xcexcmxcfx86) having a simple plane form, a cross pattern, etc. (200-300 xcexcm square)) provided at the center of the master disk 7 immediately before the magnetic medium 3 touches the master disk 7, and the position of the master disk 7 is adjusted such that the center of the magnetic medium 3 can match the center of the master disk 7, thereby setting the magnetic medium 3 closely touching the master disk 7.
Practically, as shown in FIG. 9, a small incandescent lamp 1 (for example, a halogen lamp) irradiates the vicinity of the positioning mark 9 from behind the chuck 4, a CCD camera 2 receives the reflected light from the positioning mark 9, and an obtained electric signal is processed into an image, thereby recognizing the position of the master disk 7.
The chuck 4 has a hollow structure, and the magnetic medium 3 is donut-shaped with an open hole at the center. Therefore, the light from behind the magnetic medium 3 can easily and directly reach the surface of the master disk 7. Inside the portion indicated by numeral 10 of the chuck 4 is hollow. Since the material (Co type alloy) of the positioning mark 9 and the material (single crystal silicon) of the substrate have different reflectance, the position of the positioning mark 9 can be easily recognized.
FIGS. 10A to 10D are sectional views of the process for forming the soft magnetic embedding patterns 8 and 9 into the surface of the silicon substrate 71 of the master disk 7. Described below is each of the processes.
FIG. 10A shows the process of applying up to 1 xcexcm of photo resist 19 onto the silicon substrate 71, and then performing exposing and developing processes using a photo mask. The pattern of the photo resist 19 after the development as shown in FIG. 10A is an inverted pattern of the final embedded soft magnetic pattern 8.
In the process shown in FIG. 10B, the surface of the silicon substrate 71 is etched by about 500 nm by using of the reactive ion etching method as shown in FIG. 10B.
In the process shown in FIG. 10C, a Co type alloy is formed as a soft magnetic film in the sputtering method. The thickness of the film is 500 nm to allow embedding as far as the etched portion on the surface of the silicon. Since the flying direction of the sputtered molecule (Co type alloy molecule) contributing to the growth of the film is controlled to be vertical to the surface of the silicon substrate 71, there arises no growth of the soft magnetic film vertical to the surface of the silicon substrate 71 as shown in FIG. 10C.
In the process shown in FIG. 10D, the substrate is soaked in a resist solvent to be dissolved. Thus, since the soft magnetic film on the solved resist is also washed away, the sectional form as shown in FIG. 10D with only the soft magnetic embedded patterns 8 and 9 remaining is obtained.
The method of positioning the center of the master disk 7 and the center of the magnetic medium 3 has been described above by referring to the basic configuration of the master disk. In the actual transfer process, a DLC (Diamond-like carbon) film is formed on the surface of the master disk 7 as a protective film (about 30 nm) for the purpose of extending the life of the master disk 7. In the master disk having the DLC film, the difference between the intensity of the reflected light from the positioning mark 9 and the reflected light from the silicon substrate 71 is small, and thereby it arises the problem to be solved that the positioning mark 9 cannot be recognized in the above mentioned conventional technology.
FIGS. 11A and 11B illustrate the problem above mentioned to be solved by the present invention. By referring to FIGS. 11A and 11B, the intensity of the reflected light from the master disk 7 is compared depending on the existence/non-existence of a DLC film.
In the master disk 7 having no DLC film formed as shown in FIG. 11A, assuming that the intensity of reflected lights 14 and 15 obtained by injecting a light 13 having the intensity of I0 to the surface of the silicon substrate 71 and the surface of the soft magnetic film 9 of the master disk 7 is respectively IS1 and IM1, the ratio of the reflected light 14 from the surface of the silicon substrate 71 to the reflected light 15 from the surfaces of the soft magnetic films 8 and 9 can be expressed by IS1/IM1.
On the other hand, in the master disk 7 having a DLC film 18 formed as shown in FIG. 11B, the reflected light obtained by irradiating the light 13 having the intensity I0 on the surface of the silicon substrate 71 of the master disk 7 contains the intensity IS2 of the light 14 which reaches the surface of the silicon substrate 71 and is reflected thereby and the intensity IC of a light 16 reflected by the surface of the DLC film 18. The intensity IS2 of the reflected light 14 shown in FIG. 11B, when compared with the intensity IS1 of the reflected light 14 shown in FIG. 11A when there is no DLC film 18, is absorbed and scattered and therefore more attenuated in the process of the incident light passing through the DLC film 18. This holds true with the IM2 of the light 15 reflected by the soft magnetic films 8 and 9. Therefore, the ratio of the intensity of the reflected light from the surface of the silicon substrate 71 to the intensity of the reflected light from the soft magnetic films 8 and 9 when there is the DLC film 18 is expressed by (IS2+IC)/(IM2+IC) Therefore, the ratio of the intensity of the reflected light from the surface of the silicon substrate 71 to the intensity of the reflected light from the soft magnetic films 8 and 9 when there is the DLC film 18 is normally closer to 1 than the ratio IS1/IM1 when there is no DLC film. With an increasing value of IC, the ratio of the intensity of the reflected light furthermore reaches asymptotically 1 (where the intensity of the reflected light from the silicon substrate surface is equal to the intensity of the reflected light from the soft magnetic film surface, and they cannot be distinguished from each other).
To improve the recognizability of the positioning mark 9, the value of (IS2+IC)/(IM2+IC) is to be set to a value apart from 1.
To solve the above mentioned problems, the purpose of the present invention aims at improving the recognizability of the positioning mark by setting closer to zero the intensity IC of the reflected light from the DLC film on the upper surface of the master disk, and by setting larger the ratio of the intensity IS2 of the reflected light from the surface of the lower silicon substrate of the master disk to the intensity IM2 of the reflected light from the positioning mark.
The intensity of the reflected light from the silicon substrate surface and the intensity of the reflected light from the soft magnetic film surface refer to a function of an optical wavelength individually. The first aspect of the present invention is based on this point, and the value of (IS2+IC)/(IM2+IC) is set a value apart from 1 to improve the recognizability of a positioning mark by limiting a light wavelength for using the positioning mark by limiting a light wavelength for using the positioning mark recognition to a predetermined wavelength range, in other words, by selectively using the wavelength which allows as smaller as possible for the intensity IC of the reflected light from the DLC film on the upper surface of the master disk, and a higher ratio of the reflected light intensity IS2 of the light reaching the surface of the lower substrate of the master disk and being reflected thereby to the intensity IM2 of the light reflected by the positioning mark.
It is desired to select the range of the wavelength of an incident light to an optical reception sensor using a wavelength selection filter.
In addition, it is desired to emit the light from the light source of a limited wavelength area to the positioning mark, and input the reflected light to the optical sensor.
Furthermore, it is desired to emit the light from the polarized light source of a limited wavelength area to the positioning mark, and input the reflected light to the optical sensor through a polarization filter.
To attain the above mentioned purpose, the second aspect of the present invention uses different materials between the positioning mark formed for position recognition on the master disk and the soft magnetic pattern in order to set the intensity IC of the reflected light from the DLC film on the upper surface of the master disk closer to zero, and to set a higher ratio of the reflected light intensity IS2 of the light reaching the surface of the lower substrate of the master disk to the intensity IM2 of the light reflected by the positioning mark.
Then, the process of forming a film for a positioning mark is added to the process of forming a film for a soft magnetic mark in the master disk producing process. In this process of forming a film for a positioning mark, it is desired to select as the material of a positioning mark a material having reflectance quite different from the reflectance of the substrate of the master disk from among various materials indicating no soft magnetism.
According to the present invention, lower reflection from the DLC film, which is a protective film for the master disk, and the largest difference in reflected light intensity between the light from the surface of the master disk substrate (silicon substrate) and the light from the surface of the positioning mark can be obtained by limiting the light for recognition of the positioning mark to a specific range of a wavelength. Thus, the recognizability of a positioning mark can be successfully improved.
Furthermore, according to the present invention, the recognizability of a positioning mark can be improved by using the difference in polarization between the lights reflected from different materials in addition to use a laser light as a light source.
In addition, according to the present invention, the material of a positioning mark can be selected based on that its reflectance can be quite different from the reflectance of the master disk substrate by setting the positioning mark patterning process independent of the soft magnetic film patterning process.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.